Pursuant to 35 USC xc2xa7xc2xa7365(c) and 120, the priority of PCT/EP 98/046855 filed Jul. 25, 1998 and German Application No. DE 197 33 021.5 filed Jul. 31, 1997 is claimed.
The invention is concerned with a fluid filtration unit constructed of thermoplastic polymer the unit having a filtration element within a two-part housing. Such filtration units are predominately employed in laboratories and in medical technologies, being known as dead-end or crossflow-filtration units, generally used for the filtration of liquids and gases as well as for sterile filtration. As a rule, they are operated as relatively small disposable units, for instance as an accessory for hypodermic injection or as a concentration tool in biological and genetic laboratories. Such filtration elements, when equipped with membrane adsorbers, facilitate the removal of contaminating materials or the recovery of valuable substances appearing only in small concentrations.
U.S. Pat. No. 3,782,083 describes a rotationally symmetric disposable gas filter formed from a two-part housing, wherein the two housing parts enclose a fluid-tight flat filtration membrane with a fluid inlet and outlet with interior inlet and outlet spaces. The housing parts are so designed in the peripheral edge area, that upon being pressed against one another, they snap together in a compression-type fit. When this is done, the filtration membrane is pressed against a concentric, projecting mounting member of one part of the housing and by melting the mounting member, the two parts of the housing are bonded together in a fluid-tight manner. When this occurs, the melt flows into the pores of the filtration membrane. A drawback to this design is that permeation of the melt into the pores of the membrane is often damaging to the membrane and to its filtration characteristics. The membrane becomes brittle in its periphery from the melt which permeates through it or, in the case of hydrophilic membranes, a case of so-called edge hydrophobicity occurs. A further disadvantage is that, because of the weakening of the membrane, filtration pressure differences greater than 3 bar cannot be withstood. One remedy proposed is the installation of an encapsulating, pressure-resistant enclosure of the outer edges of the housing parts applied in a spray along the periphery of the membrane, in accord with EP 0 325 712 A1; but this entails additional material and labor costs.
EP 0 118 601 B1 teaches edge hydrophobicity in hydrophilic membranes may be avoided if the surface of the hydrophilic membranes are so bound to the housing parts by plastic welding that the liquified, melted plastic does not permeate the membrane filter material. The disadvantage of this is that in the case of pressure differences of more than 3 bar, the housing may become so deformed that the surface connection becomes unsealed and the filtration unit must be discarded.
Thus, the present invention has the object of creating a filtration unit from a two-part plastic housing, which is capable of filtration of fluids with pressure differentials up to 10 bar and wherein the filtration element is so bound to the housing, that none of the foregoing disadvantages of the prior art occur. An additional object lies in the creation of a simple inexpensive procedure for the manufacture of the filtration unit so that it is justifiably treated as disposable.
The foregoing objects and advantages are achieved by the provision of a filtration unit with a filtration element situated in a housing of two interconnecting, mutually bonded parts and the housing is so divided into inlet and outlet sides by housing plenums with fluid connection fittings, that the feed side of the filtration element is proximal to the inlet plenum and its permeate is proximal to the outlet plenum. Further, the peripheral edge surface of the feed side of the filtration element is bonded fluid-tight with the first housing part, while the peripheral edge surface of the permeate side of the filtration element is pressed against a closed, peripherally running, flanged area of the second housing part. In a second aspect, the present invention provides a method of making the inventive filtration unit. Surprisingly, it has been discovered that the inventive filtration unit possesses excellent structural strength and is capable of filtration of fluids with pressure differentials of up to 10 bar.